In industries concerned with earth formation boreholes, such as hydrocarbon recovery and gas sequestration, for example, it is not uncommon for various operations to utilize a temporary or permanent plugging device. Sometimes it is desirable to plug the borehole at a specific location and then to later remove the plug. Systems employing droppable members, such as balls, for example, are typically used for just such a purpose. The ball is dropped to a ball seat positioned at the desired location within the borehole thereby creating the desired plug. Subsequently, reversing fluid flow and pumping the ball out in a direction opposite to that in which it was introduced can remove the plug. To facilitate this pumping operation balls made of relatively low density materials, such as, plastic, fiberglass, phenolic, composite or ceramic, for example, may be used as opposed to heavier balls made of solid metal, for example.
Balls made of these lower density materials, however, are susceptible to extrusion through a ball seat due to deformation of the ball under high loads. Since extrusion of the ball removes the desired plug, and can create an undesirable obstruction at other locations within the borehole, devices and systems that decrease the potential for such drawbacks would be well received in the art.